Applying electric pulses through a laser induced plasma channel for use in a 3-d metal printing process

ABSTRACT

A method of fabricating an object by additive manufacturing is provided. The method includes irradiating a portion of powder in a powder bed, the irradiation creating an ion channel extending to the powder. The method also includes applying electrical energy to the ion channel, wherein the electrical energy is transmitted through the ion channel to the powder in the powder bed, and energy from the irradiation and the electrical energy each contribute to melting or sintering the portion of the powder in the powder bed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. application Ser. No.15/794,854 entitled “Applying Electric Pulses Through a Laser InducedPlasma Channel for Use in a 3-D Metal Printing Process”, filed Oct. 26,2017, the entire disclosure of which is hereby expressly incorporated byreference herein.

INTRODUCTION

The present invention generally relates to an additive manufacturing(AM) method and apparatus to perform additive manufacturing processes.More specifically, the present invention relates to a method andapparatus for applying electric pulses through a laser induced plasmachannel for use in a 3-D metal printing process. As such, a continuousprocess of additively manufacturing a large annular object or multiplesmaller objects simultaneously, such as but not limited to components ofan aircraft engine, may be performed.

BACKGROUND

AM processes generally involve the buildup of one or more materials tomake a net or near net shape (NNS) object, in contrast to subtractivemanufacturing methods. Though “additive manufacturing” is an industrystandard term (ASTM F2792), AM encompasses various manufacturing andprototyping techniques known under a variety of names, includingfreeform fabrication, 3D printing, rapid prototyping/tooling, etc. AMtechniques are capable of fabricating complex components from a widevariety of materials. Generally, a freestanding object can be fabricatedfrom a computer aided design (CAD) model. A particular type of AMprocess uses an irradiation emission directing device that directs anenergy beam, for example, an electron beam or a laser beam, to sinter ormelt a powder material, creating a solid three-dimensional object inwhich particles of the powder material are bonded together. Differentmaterial systems, for example, engineering plastics, thermoplasticelastomers, metals, and ceramics are in use. Laser sintering or meltingis a notable AM process for rapid fabrication of functional prototypesand tools. Applications include direct manufacturing of complexworkpieces, patterns for investment casting, metal molds for injectionmolding and die casting, and molds and cores for sand casting.Fabrication of prototype objects to enhance communication and testing ofconcepts during the design cycle are other common usages of AMprocesses.

Selective laser sintering, direct laser sintering, selective lasermelting, and direct laser melting are common industry terms used torefer to producing three-dimensional (3D) objects by using a laser beamto sinter or melt a fine powder. For example, U.S. Pat. Nos. 4,863,538and 5,460,758, which are incorporated herein by reference, describeconventional laser sintering techniques. More accurately, sinteringentails fusing (agglomerating) particles of a powder at a temperaturebelow the melting point of the powder material, whereas melting entailsfully melting particles of a powder to form a solid homogeneous mass.The physical processes associated with laser sintering or laser meltinginclude heat transfer to a powder material and then either sintering ormelting the powder material. Although the laser sintering and meltingprocesses can be applied to a broad range of powder materials, thescientific and technical aspects of the production route, for example,sintering or melting rate and the effects of processing parameters onthe microstructural evolution during the layer manufacturing processhave not been well understood. This method of fabrication is accompaniedby multiple modes of heat, mass and momentum transfer, and chemicalreactions that make the process very complex.

FIG. 1 is a diagram showing a cross-sectional view of an exemplaryconventional system 100 for direct metal laser sintering (“DMLS”) ordirect metal laser melting (DMLM). The apparatus 100 builds objects, forexample, the part 122, in a layer-by-layer manner by sintering ormelting a powder material (not shown) using an energy beam 136 generatedby a source 120, which can be, for example, a laser for producing alaser beam, or a filament that emits electrons when a current flowsthrough it. The powder to be melted by the energy beam is supplied byreservoir 126 and spread evenly over a powder bed 112 using a recoaterarm 116 travelling in direction 134 to maintain the powder at a level118 and remove excess powder material extending above the powder level118 to waste container 128. The energy beam 136 sinters or melts a crosssectional layer of the object being built under control of anirradiation emission directing device, such as a galvo scanner 132. Thegalvo scanner 132 may include, for example, a plurality of movablemirrors or scanning lenses. The speed at which the laser is scanned is acritical controllable process parameter, impacting how long the laserpower is applied to a particular spot. Typical laser scan speeds are onthe order of 10 to 100 millimeters per second. The build platform 114 islowered and another layer of powder is spread over the powder bed andobject being built, followed by successive melting/sintering of thepowder by the laser 120. The powder layer is typically, for example, 10to 100 microns. The process is repeated until the part 122 is completelybuilt up from the melted/sintered powder material.

The laser 120 may be controlled by a computer system including aprocessor and a memory. The computer system may determine a scan patternfor each layer and control laser 120 to irradiate the powder materialaccording to the scan pattern. After fabrication of the part 122 iscomplete, various post-processing procedures may be applied to the part122. Post processing procedures include removal of excess powder by, forexample, blowing or vacuuming. Other post processing procedures includea stress release process. Additionally, thermal and chemical postprocessing procedures can be used to finish the part 122.

Current selective laser melting 3-D printing processes have manydisadvantages when compared with standard manufacturing processes. Thesedisadvantages include, for example, reduced strength due to non-completesintering of metal powder particles (common for AM processing) and highlevels of residual stresses due to highly concentrated localized heatapplication. Other disadvantages pertain to porosity issues which haverecently been observed in the development of cold plates used to coolhigh power electronic power conversion products that provide thermalmanagement to SiC electronic components.

FIG. 2 is an illustration of laser power applied to a target inaccordance with conventional methods and apparatuses of additivemanufacturing. A laser power supply such as the laser power supply inFIG. 2, for example, may emit approximately 80 watts of power.Conversion of electrical energy to laser typically results in a 75percent loss in power. That is, only 25 percent of the power supplied tothe 80 watt laser (i.e., 20 watts) is converted to energy reaching thepowder bed. An additional loss of 30 percent loss occurs upon meltingpowder using the laser. That is, only 70 percent of the laser's 20 watts(i.e., 14 watts) is utilized to melt the metal powder.

Thus, conventional lasers used in AM are inefficient. There remains aneed to increase the heating efficiency of lasers used in AM along witha more rapid manufacturing process.

SUMMARY

The following presents a simplified summary of one or more aspects ofthe present disclosure to provide a basic understanding of such aspects.This summary is not an extensive overview of all contemplated aspectsand is intended to neither identify key or critical elements of allaspects nor delineate the scope of any or all aspects. Its purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

The foregoing and/or other aspects of the present invention may beachieved by a method of fabricating an object by additive manufacturing.In one aspect, the method includes irradiating a portion of powder in apowder bed, wherein the irradiation creates an ion channel extending tothe powder. The method also includes applying electrical energy to theion channel, wherein the electrical energy is transmitted through theion channel to the powder in the powder bed, wherein energy from theirradiation and the electrical energy each contribute to melting orsintering the portion of the powder in the powder bed.

The foregoing and/or other aspects of the present invention may beachieved by an apparatus for additive manufacturing an object. Theapparatus includes a powder dispenser, a platform on which the object isbuilt in a powder bed, and an irradiation source irradiating a portionof powder in the powder bed, the irradiation creating an ion channelextending to the powder. The apparatus also includes a power sourceapplying electrical energy to the ion channel, the electrical energybeing transmitted through the ion channel to the powder in the powderbed. Energy from the irradiation and the electrical energy eachcontribute to melting or sintering the portion of the powder in thepowder bed.

The foregoing and/or aspects of the present invention may also beachieved by a method of fabricating an object by additive manufacturing.In one aspect, the method includes (a) depositing a given layer ofpowder in a powder bed; (b) irradiating the given layer of powder in thepowder bed, wherein the irradiation creates an ion channel extending tothe given layer; (c) applying electrical energy to the ion channel,wherein the electrical energy is transmitted through the ion channel tothe given layer of powder in the powder bed; (d) depositing a subsequentlayer of powder; and (e) repeating steps (a)-(d) until the object isformed in the powder bed.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more example aspects ofthe present disclosure and, together with the detailed description,explain their principles and implementations.

FIG. 1 is an illustration of a conventional apparatus for DMLM using apowder bed;

FIG. 2 is an illustration of laser power applied to a target inaccordance with conventional methods and apparatuses of additivemanufacturing;

FIG. 3 is an illustration of an additive manufacturing apparatusaccording to an embodiment of the present invention;

FIG. 4 is an illustration of laser and electric power applied to atarget according to an embodiment of the present invention; and

FIG. 5 is an illustration of laser and electric power applied to atarget according to another embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. For example, the present invention provides a preferred methodfor additively manufacturing metallic components or objects, andpreferably these components or objects are used in the manufacture ofjet aircraft engines. In particular, large, annular components of jetaircraft engines can be advantageously produced in accordance with thisinvention. However, other components of an aircraft and othernon-aircraft components may be prepared using the apparatuses andmethods described herein.

According to an aspect, the present invention provides a method ofapplying electric pulses through a laser induced plasma channel toimprove the consolidation of powder metal by reducing residual stressesduring the DMLS process. For example, the method may include irradiatinga portion of powder in a powder bed, wherein the irradiation creates anion channel extending to the powder. The method may also includeapplying electrical energy to the ion channel, wherein the electricalenergy is transmitted through the ion channel to the powder in thepowder bed, and wherein energy from the irradiation and the electricalenergy each contribute to melting or sintering the portion of the powderin the powder bed. In addition, the laser as in the application of alaser operating in the ultraviolet portion of the electromagneticspectrum is used solely to create the plasma channel for the electricalpulse to pass through. According to an exemplary embodiment, theelectrical pulse is used for the sintering and melting process withoutthe aid of the laser for assisting in the sintering and melting process.

FIG. 3 is an illustration of an additive manufacturing apparatus,according to an embodiment of the present invention. In FIG. 3, anapparatus 300 may be provided to build a part 302 layer-by-layer in apowder bed 304. The part 302 may be built by using a laser power supply306. The laser power supply 306 supplies power to a laser 308 that emitsa beam to mirror 310. The beam reflects off the mirror 310 to aconductive element 312. The conductive element 312 may be, for example,an optical lens or mirror capable of focusing the energy of the laserbeam emitted by the laser 308. The apparatus 300 also includes a powersupply 316 to provide an electric pulse to the conductive element 312.The power supply 316 has a positive voltage source V+ at one endconnected to the conductive element 312 for providing the electric pulseto the conductive element 312. The other end of the power supply 316 isgrounded GND and connected to the powder bed 304. The laser power supply306 and the power supply 316 may be connected to a functional generator320 and controlled by a programmable controller 318. The controller 318may be, for example, a programmable proportional, integral, differentialcontroller that provides dual laser and electrical power pulse control.

According to an aspect, the laser 308 emits the laser beam into a volumeof air space above the powder bed 304. The laser beam emitted by thelaser 308 rapidly excites and ionizes surrounding gases, atoms and formsan ionization path to guide the electric pulses provided by the powersupply 316. The ionized surrounding gases form plasma which forms anelectrically conductive uniform plasma channel 314. The electric pulsesprovided by the power supply 316 may then be applied through the plasmachannel 314 to heat and bond metal powder in the powder bed 304 to buildthe part 302. Thus, according to the exemplary embodiment, when electricpulses are applied to metals undergoing deformation by optional laserheating, the deformation resistance may be significantly reduced withincreased plasticity. It may be appreciated that the laser beam andelectric pulse may be applied simultaneously or staggered one after theother, after a short delay.

FIG. 4 is an illustration of a laser and electric power supply of 120watts applied to a target according to an embodiment of the presentinvention. As shown in FIG. 4, a laser power supply having 80 watts andan electric power supply having 40 watts may combine to apply 120 wattsof power to a target according to an exemplary embodiment of the presentinvention. Due to the losses associated with converting electricalenergy to a laser beam, only approximately 25 percent of the poweremitted by the 80 watt laser power supply may be utilized (i.e., 20watts). When the laser power reaches the target, approximately 70percent of the 20 watts from the laser is utilized melting the powder;that is, approximately 14 watts of power applied from the 80 watt laserpower supply. According to an aspect, the electric power supply mayapply an electric pulse of 40 watts to the laser induced plasma channelcreated by the 80 watt laser power supply. Approximately 90% of the 40watts applied from the electric power supply may be utilized (i.e., 36watts) at the powder bed. As such, the 36 watts of power from theelectric power supply combined with the 14 watts of power from the laserpower supply allows for 50 watts of total power to be applied to meltthe target in accordance with the exemplary embodiment of the presentinvention. Thus, additive manufacturing in accordance with the presentexemplary embodiment using electric pulses through a laser inducedplasma channel, may apply approximately four times more heat to a targetthan conventional additive manufacturing methods.

FIG. 5 is an illustration of a laser and electric power supply of 80watts applied to a target according to another embodiment of the presentinvention. As shown in FIG. 5, a laser power supply having 40 watts andan electric power supply having 40 watts may combine to apply 80 wattsof power to a target according to an exemplary embodiment of the presentinvention. Due to the loss of power associated with convertingelectrical energy to a laser beam, only approximately 25 percent of thepower emitted by the 40 watt laser power supply is utilized (i.e., 10watts) at the powder bed. When the laser power reaches the target,approximately 70 percent of the 10 watts utilized may be applied to meltthe target; that is, approximately 7 watts of power from the 40 wattlaser power supply. According to an aspect, the electric power supplymay apply an electric pulse of 40 watts to the laser induced plasmachannel created by the 40 watt laser power supply. Approximately 90% ofthe 40 watts applied from the electric power supply may be utilized(i.e., 36 watts). As such, the 36 watts of power from the electric powersupply combined with the 7 watts of power from the laser power supplyallows for 43 watts of total power to be applied to melt the target inaccordance with the exemplary embodiment of the present invention. Inthis exemplary embodiment, approximately three times more heat may beapplied to a targeted area than conventional additive manufacturingmethods.

In accordance with the above-described, the present invention provides a3-D printing process that may increase reliability of the manufacturedpart, improve the mechanical properties of printed metal parts, andimprove efficiency of the selective sintering process. The presentinvention may provide several advantages of using additive manufacturingfor 3-D metal printing such as, but not limited to, reduced deformationresistance, improved plasticity, simplified processes, increased systemelectrical energy efficiency, lower cost through improved yield, loweredproduct defects minimizing voids, and improved affected metalproperties.

This written description uses examples to disclose the invention,including the preferred embodiments, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.Aspects from the various embodiments described, as well as other knownequivalents for each such aspect, can be mixed and matched by one ofordinary skill in the art to construct additional embodiments andtechniques in accordance with principles of this application.

1. An apparatus for additive manufacturing an object, comprising: apowder dispenser; a platform on which the object is built in a powderbed; an irradiation source irradiating a portion of powder in the powderbed, the irradiation creating an ion channel extending to the powder;and a power source applying electrical energy to the ion channel, theelectrical energy being transmitted through the ion channel to thepowder in the powder bed, wherein energy from the irradiation and theelectrical energy each contribute to melting or sintering the portion ofthe powder in the powder bed.
 2. The apparatus of claim 1, wherein theirradiation source is a laser power supply.
 3. The apparatus of claim 1,wherein the ion channel is a laser induced plasma channel.
 4. Theapparatus of claim 1, wherein the power source is an electrical powersupply.
 5. The apparatus of claim 1, wherein the apparatus furthercomprises an electrically conductive element.
 6. The apparatus of claim5, wherein the electrically conductive element is a lens or mirror. 7.The apparatus of claim 1, wherein the energy from the irradiation andelectrical energy are controlled to contribute to the melting orsintering the portion of the powder in the powder bed simultaneously orconsecutively.